Method and apparatus for improving vehicle fuel economy with energy storage efficiency model

Abstract

A method is described for improving fuel economy in a vehicle having an engine, a generator driven by the engine, and an energy storage unit by using an energy storage efficiency model. The method includes evaluating a current efficiency state of the engine, evaluating a current efficiency state of the generator, evaluating a current efficiency state of the energy storage unit, and, controlling the generator to provide an optimized voltage output, based on the results of the evaluations and the energy storage efficiency model. A voltage regulator implementing this method is also described.

What is claimed is: 
     
         1 . A method of improving fuel economy in a vehicle comprising an engine, a generator driven by the engine, and an energy storage unit by using an energy storage efficiency model, the method comprising:
 evaluating a current efficiency state of the engine;   evaluating a current efficiency state of the generator;   evaluating a current efficiency state of the energy storage unit; and   controlling the generator to provide an optimized voltage output, based on the results of the evaluations and the energy storage efficiency model.   
     
     
         2 . The method of  claim 1 , further comprising determining whether the vehicle is decelerating and, if so, maximizing voltage output so as to accumulate maximum charge in the energy storage unit. 
     
     
         3 . The method of  claim 1 , wherein evaluating the current efficiency state of the engine comprises determining whether an increase in generator load will result in a positive or negative change in efficiency, given a current torque output of the engine. 
     
     
         4 . The method of  claim 3 , wherein evaluating the current efficiency state of the engine further comprises using an efficiency curve to determine whether an increase in generator load will result in a positive or negative change in efficiency. 
     
     
         5 . The method of  claim 3 , wherein evaluating the current efficiency state of the generator comprises determining generator rotor speed and field current. 
     
     
         6 . The method of  claim 3 , wherein evaluating the current efficiency state of the energy storage unit comprises determining a current regulator output voltage, a state of charge of the energy storage unit, and a temperature of the energy storage unit. 
     
     
         7 . The method of  claim 3 , wherein the energy storage efficiency model indicates that voltage output will be set sufficiently high so as to accumulate charge in the energy storage unit if:
 a) a state of charge of the energy storage unit is below a minimum threshold;   b) the efficiency state of the engine is positive, the efficiency states of the generator and energy storage unit are high, and the state of charge of the energy storage unit is below an overcharge threshold; or   c) the efficiency state change of the engine is positive, the efficiency state of the generator is high, and the state of charge of the energy storage unit is below a midpoint threshold.   
     
     
         8 . The method of  claim 6 , wherein the energy storage efficiency model indicates that voltage output will be set sufficiently high so as to maintain a state of charge in the energy storage unit if:
 a) the efficiency state change of the engine is positive, the efficiency states of the generator and energy storage unit are high, and the state of charge of the energy storage unit is above an overcharge threshold; or   b) the efficiency state change of the engine is positive and the efficiency state of the generator is low.   
     
     
         9 . The method of  claim 8 , wherein the energy storage efficiency model indicates that the generator should be deactivated if the efficiency state change of the engine is negative or the efficiency state of the generator is low, and the state of charge of the energy storage unit is above the minimum threshold. 
     
     
         10 . A voltage regulator comprising:
 a processor and connected memory; the processor being adapted to:   evaluate a current efficiency state of a connected engine;   evaluate a current efficiency state of a connected generator;   evaluate a current efficiency state of a connected energy storage unit; and   based on the results of the evaluations and an energy storage efficiency model, control the connected generator to provide an optimized voltage output.   
     
     
         11 . The voltage regulator of  claim 10 , wherein the connected generator is an alternator. 
     
     
         12 . The voltage regulator of  claim 10 , wherein the connected energy storage unit is a battery. 
     
     
         13 . The voltage regulator of  claim 10 , wherein evaluating the current efficiency state of a connected engine comprises determining an efficiency curve of the connected engine. 
     
     
         14 . The voltage regulator of  claim 13 , wherein the efficiency curve establishes a range in which an increase in engine torque does not decrease overall efficiency of the engine. 
     
     
         15 . The voltage regulator of  claim 10 , wherein the energy storage efficiency model indicates that voltage output will be set sufficiently high so as to accumulate charge in the energy storage unit if:
 a) a state of charge of the energy storage unit is below a minimum threshold;   b) the efficiency state change of the engine is positive, the efficiency states of the generator and energy storage unit are high, and the state of charge of the energy storage unit is below an overcharge threshold; or   c) the efficiency state change of the engine is positive, the efficiency state of the generator is high, and the state of charge of the energy storage unit is below a midpoint threshold.   
     
     
         16 . The voltage regulator of  claim 15 , wherein the energy storage efficiency model indicates that voltage output will be set sufficiently high so as to maintain a state of charge in the energy storage unit if:
 a) the efficiency state change of the engine is positive, the efficiency states of the generator and energy storage unit are high, and the state of charge of the energy storage unit is above an overcharge threshold; or   b) the efficiency state change of the engine is positive and the efficiency state of the generator is low.   
     
     
         17 . The voltage regulator of  claim 16 , wherein the energy storage efficiency model indicates that the generator should be deactivated if the efficiency state change of the engine is negative or the efficiency state of the generator is low, and the state of charge of the energy storage unit is above the minimum threshold.